More than 50 million Americans suffer from allergies, making them the sixth leading cause of chronic disease in the United States, and responsible for 3.8 million lost work or school days per year. Common house dust is a leading cause of allergies. Although there are many components in house dust that may be allergenic, the most common culprit by far is the dust mite, which is second only to pollen overall in causing allergic reactions. More than 15 groups of house dust mite allergens (proteins) have been identified from extracts and feces of dust mites. The group 1 and group 2 proteins are the major allergens, accounting for 60 to 90% of the activity.
Furthermore, dust mite allergens are closely related to the onset of asthma. Asthma is a serious and potentially fatal condition that is especially critical in children under age 13. The American Lung Association estimates that 32.5 million Americans (approx. 11.2%) have been diagnosed with asthma. 14.2% of American children between 5 and 17 years of age had asthma is in 2005. It has been shown that most children with exacerbation of asthma have been exposed to high levels of mite allergens, and that continuous exposure can result in hospital readmission. The highest levels of allergens are found in bedding (blankets, sheets, spreads, pillow cases, etc.), placing humans at high risk of inhaling the offending proteins. A nationwide survey conducted by the National Institute of Environmental Health Sciences (NTRHS) and the US Department of Housing and Urban Development in 1998 and 1999 reports that 84% of U.S. homes have detectable levels of mite allergens; about half have levels sufficient to trigger allergic reactions; and a quarter of U.S. homes have high enough allergen level to cause asthma. The cost of asthma in 2007 is projected to reach $19.7 billion ($14.7 direct, $5 indirect). In New York's Harlem neighborhood, 25.5% of children under age 13 suffer from asthma. The sensitization level of the group 1 allergen in adults is 2 μg allergen/g dust, and 10 μg allergen/g dust enhances asthma symptoms. For children, the sensitization level could be as low as 50 ng/g, far below the general sensitization level.
Dust mites are eight-legged arachnids, relatives of the spider. The American house dust mite (Dermatophagoides farinae, Df) and the European house dust mite (Dermatophagoides pteronyssinus, Dp) are the two most common species in the United States. Dust mites progress through the egg, larval and nymph stages in about 25 days to become microscopic adults about 0.3 mm in length. Adults live two to three months, during which time the female can lay 25 to 50 eggs every two to three weeks. They feed on shed scales of human skin. Only environments with a relative humidity of less than 50% year round are safe from these allergy causers. Mites live in carpet, upholstered furniture, and bedding. The allergenic proteins are actually present in dust mite feces and each dust mite produces about twenty waste particles per day. More than 100,000 particles can be present in a single gram of dust. Particles continue to cause allergy symptoms long after the dust mites themselves are dead. Mite allergens can cause or exacerbate three major diseases: asthma, perennial rhinitis, and atopic dermatitis. The consequences of which can be fatal.
More than 15 groups of house dust mite allergens have been identified from extracts and feces of Dp and Df dust mites. The group 1 (Der p 1 and Der f 1) and group 2 (Der p 2 and Der f 2) proteins are the major allergens, accounting for 60 to 90% of IgE binding activity of the dust mite sera. The group 2 allergen levels are comparable to the levels of the group I allergens. The group 1 allergens are proteins (MW 25 kDa) with cysteine protease activity. Proteolytic activity is an important factor for sensitization by Der p 1. Der p 1 cleaves the CD23 IgE receptors on B-cells and the CD25 subunit of the IL-2 receptor on T-cells, which further promote the Th2 response and IgE-mediated hypersensitivity (allergy).
At present, there are few effective options for patients with severe allergic or asthmatic reactions. Allergen avoidance (i.e. relocation to allergy-free environments) has been shown to result in reduced asthma symptoms. Obviously, moving people and families into special environments is both expensive and socially disruptive. Conventional allergen avoidance measures include washing of fabrics in hot water, using allergen impermeable covers, regular vacuuming, and elimination of carpet and upholstered furnishings. Washing is recommended to control dust mite allergen levels. Washing can remove soluble allergens, and hot water will kill dust mites if the temperature is higher than 55° C. Many items of bedding cannot be washed in a household washer, and ordinary U.S. household washers operate with warm or cold water that does not ensure mite death. D. pteronyssinus is highly resistant to warm water, detergent and chlorine. A 4 hour soak in a 35° C. detergent and chlorine (0.35%) solution achieved only 34% mortality of D. pteronyssinus. Even with the addition of 0.03% benzyl benzoate, approximately 50 out of 10,000 mites survived. Additional concerns about washing include the transference of mites between infested and mite-free items, and the fact that some fabrics will shrink or be damaged when washed at 55° C. Chemical-based dry cleaning effectively kills mites and can be used to clean delicate clothing and some bedding items, but has been shown to reduce the allergen activity by only 70%, because the residual proteins are not deactivated by dry cleaning. Semi-impermeable mattress covers are said to control allergen levels for at least 12 weeks, leading to improved symptoms. However, this method is not low-maintenance as it requires regular washing of the case at T>55° C. and periodic wiping.
Using acaricides to kill dust mites, therefore eliminating the source of allergens, is another method that has been proposed to reduce allergen levels. Heller-Hauput and Busvine tested 15 chemicals for ability to kill D. farinae. In the order of potency, Lindane, pirimiphosmethyl, and benzyl benzoate are the most effective. Toxicity studies and a history of use for treatment of scabies indicate that Lindane and benzyl benzoate can safely be used to kill dust mites. However, acaricides do not deactivate residual allergy-causing mite proteins. Solid benzyl benzoate foam and powders (60 g/m2, then vacuumed) have been tested on mattresses and blankets in Germany for their efficiency of reducing Der p 1 and der f 1 allergens. The tests revealed that powered benzyl benzoate only works on blankets possibly due to the difficulty of the solid material penetrating the mattresses which are much thicker than blankets. A similar study in Italy reported that benzyl benzoate in foam form is also not effective in decreasing dust mite allergen again possibly due to insufficient penetration.
Prior art indicates that dense phase CO2 can kill various types of cells, including microorganisms (bacteria, bacterial spores, fungus) and mammalian cells, with the help from selected liquid chemicals including water and hydrogen peroxide. It takes hours to kill resistant species such as bacterial spores. However, it only takes minutes to kill animal cells such as mammalian cells. Therefore, dense phase CO2 can kill living dust mites quickly.
It is the protein secreted by dust mites that are the main cause of allergic reactions and asthma. These proteins secreted by Dermatophagoides pteronyssinus include a spectrum of mite allergens denominated as der p1 to der p9. Among these, der p1 and der p2 are the major allergens. Partial inactivation of proteins by dense phase CO2 has been widely documented in the literature. However, no complete inactivation of enzymes with CO2 has been previously reported.
Current state of the art measures to prevent mite allergen-induced diseases include frequent vacuuming with high filtration vacuum cleaners, UV light irradiation, topical application of an insecticide to kill the dust mite, covering all beds with micro-porous dust-proof or allergen impermeable covers, weekly washing of bedding with hot water and freezing non-washable beddings overnight, and removing carpets from all rooms. However most prior art suffers from many drawbacks. Vacuum cleaners and insecticides suffer from the inability to penetrate deep into carpets. Also, carpets usually cannot be removed and frozen; or be washed with hot water. It is not feasible to cover entire household carpets with impermeable covers. In addition, water washing, even with hot water, will not kill dust mites; and impermeable covers appear clinically ineffective in adults with asthma.
As such, a need exists for the eradication of dust mites that overcomes the disadvantages of prior art methods.